Problems have arisen in stabilizing loads on flatbed vehicles when shipping stacked product. In particular, difficulties have been encountered in shipping vinyl siding on flatbed trucks. Vinyl siding normally is shipped in cardboard boxes containing 24 pieces of siding, the boxes being approximately 131/2 inches wide, 5 inches high, and 12 feet 6 inches long. Attempts have been made to stabilize such boxes of vinyl siding by stacking them in units that are four units wide and seven units high and containing them with wooden frameworks, preferably reinforced at the corners with metal L-shaped brackets. Such formed units may be stacked two high, two wide on a flatbed truck, and up to a total of six units may be conveniently thus carried when strapped down. However, the loads tend to shift even when so secured creating a traffic hazard in that a truck could lose a part of its load and also increasing costs since trucks have to stop and reload or reposition the units.